WhatsApp: A $19 billion bet for Facebook

Zuckerberg said the service 'doesn't get as much attention in the U.S. as it deserves.' | AP Photo

In that regard, the acquisition makes sense for 10-year-old Facebook as it looks to attract its next billion users while keeping its existing 1.23 billion members, including teenagers, interested. The company is developing a "multi-app" strategy, creating its own applications that exist outside of Facebook and acquiring others. It released a news reader app called Paper earlier this month, and has its own messaging app called Facebook Messenger.

"Facebook seems to be in acknowledgement that people are using a lot of different apps to communicate," said eMarketer analyst Debra Aho Williamson. "In order to continue to reach audiences, younger in particular, it needs to have a broader strategy...not put all its eggs in one basket."

"We want to provide the best tools to share with different sized groups and in different contexts and to develop more mobile experiences beyond just the main Facebook app, like Instagram and Messenger," Zuckerberg said in a conference call. "This is where we see a lot of new growth as well as a great opportunity to better serve our whole community."

WhatsApp, a messaging service for smartphones, lets users chat with their phone contacts, both one-on-one and in groups. The service allows people to send texts, photos, videos and voice recordings over the Internet. It also lets users communicate with people overseas without incurring charges for pricey international texts and phone calls. It's free to use for the first year and costs $1 per year after that. It has no ads.

"It'll be tempting to read this as a sign Facebook is scared of losing teens," said Forrester analyst Nate Elliot in an emailed note. "And yes, the company does have to work hard to keep young users engaged. But the reality is, Facebook always works hard to keep all its users engaged, no matter their age. Facebook is tireless in its efforts to keep users coming back."

Asked about the demographics of WhatsApp's users, Facebook finance chief David Ebersman said that, "if you look at the kind of penetration that WhatsApp has achieved, it sort of goes without saying that they have good penetration across all demographics, we would imagine.

That said, "it's not a service that asks you to tell them your age when you sign up," he added.

Facebook's shares fell $1.82, or 2.7 percent, to $66.24 in after-hours trading Wednesday after the deal was announced. Earlier in the day, the stock hit a 52-week high of $69.08.